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I have a file with the following permissions:

root:data, and chmod set to 775.

My normal user, let's call him boby, is in the data group.

Why can't I delete the file with the user boby?

 rwxrwxr-x 18 root data 4096 2011-12-30 22:02 storage
 my user is in the group data but can't write into storage
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5 Answers 5

Because deleting a file you are not just modifying the file but also modifying the directory.

So if your file is:

rwxrwxr-x

You would be able to do:

cp /dev/null <filename>

But if your directory permissions are:

rwxr-xr-x  root  data  <directory name>

Then system will prevent you removing the file.

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I have drwxrwxr-x on the directory, I think it has something to do with the d in front –  user56301 Dec 30 '11 at 19:55
2  
@user56301 d just indicates that this file is a directory. What's the ownership of the directory? –  Karlson Dec 30 '11 at 19:58
    
drwxrwxr-x 18 root data –  user56301 Dec 30 '11 at 19:59
    
Try running as user boby the following: cd <directory> ; touch test_file ; rm test_file –  Karlson Dec 30 '11 at 20:02
    
@user56301 can you create a file in that directory? if you can not, then you definitely can't delete a file there. –  Rich Homolka Dec 30 '11 at 20:03

File deletion is based on directory perms, not file perms (*).

Do you have write permissions on the directory that contains the file?

(*) Caveat, you can have a directory where you enforce that only the owner of the file can delete it. This is useful for temp dirs.

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If the containing directory does not permit the user boby or the data group to write to it, then that would explain this behavior.

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So the entire path needs group permission? It works like that. –  user56301 Dec 30 '11 at 20:06
    
@user: Not the entire path - just the file's immediate parent directory. You are only modifying the directory's contents. The higher parents do not matter at all. –  grawity Dec 30 '11 at 20:08
    
I update the answers –  user56301 Dec 30 '11 at 20:09
    
This is not exactly true. You only need write perms on the containing directory. The perms can be any of user, group, or other, it doesn't have to be group perms that allow you. –  Rich Homolka Dec 30 '11 at 20:12
    
@Rich: AFAIK, only one set is checked. If you are the owner, the system will only check 'owner' perms, not 'group' nor 'others'. If you are in the group, the system won't check 'others' perms. (touch foo; chmod 6 foo; ls -l foo; cat foo) –  grawity Dec 30 '11 at 20:24

I tried the same thing, and ran into the same problem.

Starting a new terminal session the problem. This can be achieved by:

  1. Logging out and logging back in
  2. Going to one of the 6 ttys (Ctrl+Alt+F1-6) (Note: Ctrl+Alt+F7 is your GUI session)
  3. using su boby to start a new session for user boby.

Cheers!

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He mentions he is already logged in as boby –  Canadian Luke Sep 5 '13 at 14:38
    
He needs to login again as boby - the old session seems to be stale and not reflect the group association changes. –  Here Be Wolves Sep 5 '13 at 15:39

I bet the file you're trying to delete is in /tmp.

See Linux - group member cannot delete file with rw permission

/tmp usually has the "sticky" aka "restricted deletion" mode set (o+t). With this mode set, only the file's owner can move or delete files in that directory regardless of any permissions.

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